In vertical electroslag welding, the workpieces to be welded are vertically aligned with a gap exposed between their parallel edges. Two molding shoes, usually of copper, are located on both sides respectively of the gap with their interiors contoured to form in conjunction with the gap a cavity into which is added a granular flux and filler metal. The filler metal is continuously supplied from a spool of consumable electrode wire. Current is passed through the electrode to form within the cavity a puddle of molten metal and slag. A driving mechanism propels the copper molding shoes, the accessory equipment to make the weld, and the consumable electrode upward along the gap resulting in the vertical progression of the weld. The speed of the driving mechanism is typically set at a speed of between about 3-10 inches per minute depending upon the welding conditions and parameters. The height of the puddle of molten metal and slag must be controlled as the molding shoes move upward. Otherwise, if the puddle remains too fluid as the shoes advance molten metal will run out from under the cavity or alternatively if the puddle height gets too high molten metal will spill over the cavity walls. Heretofore, puddle height regulation was accomplished by varying the electrode wire feed speed in response to variations in the level of electrode current. At higher travel speeds however, regulation was unsatisfactory. A more responsive and more reliable control was found in directly varying the speed of the driving mechanism.
Accordingly, it is the principle object of the present invention to provide a speed control for regulating the molten weld puddle height independent of the wire feed motor speed and in direct response to electrode current.
It is a further object of the present invention to provide a speed control for electroslag vertical welding which regulates the speed of advance of the cavity forming molding shoes in direct response to the welding current but electrically remote therefrom.